High Speed Data; Dual Tone Multiple Frequency (Dtmf) Data - Motorola GTX/LCS 2000 Service Manual

High Speed Data

Dual Tone Multiple Frequency
(DTMF) Data
This drives a tone generator inside U0201 which generates a staircase
approximation to a PL sine wave or DPL data pattern. This internal waveform is
then low-pass filtered and summed with voice or data. The resulting summed
waveform then appears on U0201-H8 (MOD IN), where it is sent to the RF board
as previously described for transmit audio. A trunking connect tone would be
generated in the same manner as a PL tone.
High speed data refers to the 3600 baud data waveforms, known as Inbound
Signalling Words (ISWs) used in a trunking system for high speed communication
between the central controller and the radio. To generate an ISW, the µP first
programs the ASFIC (U0201) to the proper filter and gain settings. It then begins
strobing U0201-G1 (TRK CLK IN) with a pulse when the data is supposed to
change states. U0201's 5-3-2 State Encoder (which is in a 2-state mode) is then
fed to the post-limiter summer block and then the splatter filter.
From that point it is routed through the modulation attenuators and then out of the
ASFIC to the RF board. MPT 1327 and MDC are generated in much the same way
as Trunking ISW. However, in some cases these signals may also pass through a
data pre-emphasis block in the ASFIC. Also these signalling schemes are based
on sending a combination of 1200 Hz and 1800 Hz tones only. Microphone audio
is muted during High Speed Data signalling.
DTMF data is a dual tone waveform used during phone interconnect operation. It
is the same type of tones which are heard when using a "Touch Tone" telephone.
There are seven frequencies, with four in the low group (697, 770, 852, 941Hz)
and three in the high group (1209, 1336, 1477Hz).
The high-group tone is generated by the µP (U0101-5) strobing U0201-G1 at six
times the tone frequency for tones less than 1440Hz or twice the frequency for
tones greater than 1440Hz. The low group tone is generated by the µP (U0101-7)
strobing U0201-G2 (DTMF CLCK) at six times the tone frequency. Inside U0201
the low-group and high-group tones are summed (with the amplitude of the high
group tone being approximately 2 dB greater than that of the low group tone) and
then pre-emphasized before being routed to the summer and splatter filter. The
DTMF waveform then follows the same path as was described for high-speed
data.
Theory of Operation 7-17